Highly selective detection of Pd²⁺ ion in aqueous solutions with rhodamine-based colorimetric and fluorescent...

In this study, we report a new class of rhodamine-based fluorescent sensors for highly selective and sensitive detection of Pd²⁺ ions in aqueous medium. A rhodamine-based palladium sensor RPS and a coumarin-rhodamine Förster resonance energy transfer (FRET)-pair based palladium sensor FPS were synthesized with the designed podand ligand for Pd²⁺ ion recognition. They showed both colorimetric change and fluorometric change in the presence of Pd²⁺ ion due to the opening of their spirolactam rings. Both chemosensors are highly selective to Pd²⁺ over the other 24 different metal ions and they are selective to palladium species in +2 oxidation state, RPS showed a 70-fold fluorescent turn-on while FPS showed a 1.75-fold ratiometric change at I₅₉₉/I₄₇₀. Furthermore, RPS showed low cell cytotoxicity and it was successfully used to image Pd²⁺ in BEAS-2B lung epithelial cells. © 2019 Elsevier Science. All rights reserved.